Method of treating well bore walls



April 8, 1941. c. F. PRUTTON 2.237.313

METHOD OF TREATING WELL BORE WALLS Filed Dec. 24, 1958 ATTORNEYS.

atentecl Apr. 8, 1941 METHOD OF TREATING WELL BORE WALLS Carl F. Prutton, Cleveland, Ohio, assignor to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application December 24, 1938, Serial No. 247,595

3 Claims.

lhe invention relates to an improved method of preparing the walls of a well bore penetrating a producing formation for the production of mineral fluids. It more particularly concerns a method of providing a channeled supporting wall for the producing portion of a well bore.

In conventional wellj drilling practice, it is customary to lower the casing string into the well bore to a point above the producing formation and cement it in place. The well is then produced in the usual manner, as by pumping. Recently, however, it has been the practice in some fields to extend the casing through the producing formation to the bottom of the well bore in order to guard against sloughing of the walls of the bore and to prevent the infiltration of water or brine from contiguous formations.- Cement is then forced up into the annular space behind the metal casing to hold it in place. To produce a well equipped in this manner, it is necessary to perforate both the casing and surrounding cement liner to allow the fluid from the producing formation to enter the well bore. This is accomplished by lowering a gun perforator of conventional type into the well through the casing to a point opposite theproducing formation and discharging steel projectiles from the gun through the casing and cement liner into the formation.

well.

the wall or cement grout to seal said pipe in place. Still other further objects of the invention will be apparent as the description proceeds.

In carrying out the method of the invention in a well which has been drilled in the stratum from which production is to be obtained, the well is first lined with a metal pipe down to a point above the producing formation and the pipe is then cemented in place. The producing formation immediately surrounding the well bore is then impregnated with a chemical solution which is of itself capable of transformation into a solid sealing mass, or capable of reacting with a solution of a chemical later introduced to form such a sealing mass. After the solution or solutions, as the case may be, have been allowed to react and solidify thus consolidating and solidifying the walls of the well bore and the formation immediately surrounding the well bore, the formation is opened to production by explosive means, such as by dischargin steel projectiles into it from a gun perforator or by setting off a charge of an explosive such as dynamite, nitroglycerin, or the like opposite the formation.

The invention, then, consists of the method hereinafter fully described and particularly pointed out in the claims, reference being made to the accompanying drawing illustrating a preferred mode of carrying out the invention in a Using a gun perforator in the above manner 30 well bore.

has a decided disadvantage that the projectiles The single figure illustrates in vertical section from the gun penetrate only a relatively short a well suitably equipped for carrying out the indistance into the formation, it being necessary vention. As shown, the upper portion of the well for them first to penetrate the steel casing and bore is cased with a metal casing 2 and passes the surrounding cement before they can reach 5 through non-productive earth and rock, the the formation. A still further disadvantage of lower portion 3 of the casing being cemented in the method lies in the fact that perforations rock stratum 4 with cement 5. The lower unmade in the conventionalcement liner surroundcased portion of the well bore 6 is shown peneing the metal casing often become partially or trating productive stratum l2 with the walls of entirely clogged or plugged due to cracking or 40 the well bore and adjacent formation impregcrumbling of the cement resulting from the shatnated with a solidified sealing-mass I. Gun pertering action of the projectiles, thus curtailing forator 8 equipped with a series of laterally dior completely stopping the inflow of oil into the rected sockets 9 and fuse lead in attached there- In addition, the cracks produced in .the' to and to an electrical device (not shown) above cement liner near the top or bottom of the producing formation'when these areas are perforated may permit the infiltration of undesirable fluids if these portions are contiguous to waterbearin'g formations.

It is, therefore, the principal object of the invention to provide an improved method of supporting the wall of a well bore adjacent a producing formation, whereby said wall may be opened to production by explosive means without the necessity of -using a metal pipe to support the ground for firing steel projectiles from the sockets is shown suspended from cable II in the well opposite the producing formation 12.

In carrying out the method of the invention, a quantity of a liquid silicate mixture of the type which is of itself capable of spontaneous transformation into a firm, solid gel after a time is introduced in the lower portion of. the well bore 6 in an amount sufficient to fill the bore of the well to a point 13 just above the producing formation 12. The liquid silicate mixture is then .is of sufi'icient fluidity to be introduced into the well bore and readily withdrawn therefrom. The non-penetrating liquid mixture introduced into the well on top of the liquid silicate mixture acts as a piston which, as pressure is applied, completely displaces the liquid silicate mixture from the bore hole into the surrounding formation immediately adjacent the bore hole. After the liquid silicate mixture has been completely displaced from the well bore into the surrounding formation, pressure is held upon the non-penetrating liquid mixture, if necessary, until the" liquid silicate mixture has solidified. The nonpenetrating liquid mixture is then withdrawn from the well and the gun perforator 8 is lowered to a point opposite the producing formation and discharged. The steel projectiles readily penetrate through the portion of the formation impregnated by the sealing agent, forming channels l4 therein through which the mineral fluid may flow into the well bore.

Various modifications of the above procedure may be employed. For example, instead of employing a gun perforator, a. charge of explosive, such as dynamite, nitroglycerin, or the like, may be lowered into the well bore through the casing and exploded opposite the impregnated formation. This leaves the consolidated walls and the surrounding formation in a fissured orchanneled condition, thus allowing the mineral fluid to flow into the well readily. 1

Among the liquid silicate mixtures capable of spontaneous transformation to a strong solid gel after a predetermined length of time are the fol,- lowing illustrative examples.

Example 1 by weight Nam-3.22 SiOe) 10-75.

Concentrated hydrochloric acid (37% by weight) 10-20 Water 12-70 Liquid silicate mixtures having a composition within the range of the above proportions spontaneously become solid, gels in from to 25 hours at 120 F. depending on the proportion of each ingredient.

Example 2 A dilute solution of sodium silicate is prepared by diluting .40 per cent sodium silicate (Nam-3.22 SiOz) with water to the specific grav- 75 15 Water ity of 1.171, giving a solution containing 19.1 per cent by weight of sodium silicate. The dilute solution of sodium silicate so prepared is then added with stirring to a solution of ammonium 5 bicarbonate, prepared by diluting with water a stock aqueous solution of ammonium bicarbonate containing 16.9 per cent by weight of the carbonate in the following proportions byvolume:

Per cent by volume Dilute solution of sodium silicate (19.1% by weight Nam-3.22 SiO-i) 5-85 Aqueous ammonium bicarbonate solution 5-8;

Liquid silicate mixtures having a composition with the range of the above proportions spontaneously become solid gels in from to 15 hours at 120 F. depending upon the proportion of each ingredient.

Although the invention has been described with particular reference to the use of a solution of a settable liquid silicate mixture as the sealing agent to be used in impregnating and consolidating the walls of the well bore'in the formation prior to opening the formation to production by explosive means, it is to be understood that other" chemical sealing agents may also be suitably employed. For example, chemical solutions of the type reactable with a second chemical solution to produce a sealing mass may also be employed in accordance with the invention.

, By successively impregnating the formation with 3 the two solutions whereby they are caused to react a sealing efiect may be produced. Illustrative examples of such chemical solutions which may be reacted in the above manner are watersoluble soaps and a solution of calcium chloride,

40 a solution of sodium sulphate and a solution of .barium chloride, and a solution of a soluble silicate and a solution of calcium chloride. Other sealing agents of a similar nature may also be employed.

Examples of non-penetrating liquid mixtures useful for displacing the sealing agent from the well bore are those liquid mixtures having a specific gravity approximately the same as, or lower than, that of the agent to be displaced into the formation. One type of such a non-penetrating liquid mixtureconsists of a solution or a dispersion of an organic jellifying material in water. By organic jellifying material is meant an organic material capable of being dispersed or dissolved in water to make a mobile liquid dispersion or solution which exhibits jellifying characteristics after a time. Suitable organic jellifying materials may be prepared from starches, such as those of cassava or rice, by mix- 0 ing them with water to form a thin paste and boiling the mixture until the starch is hydrolyzed. The fcooked starch is dried at about 80 C.'and the dried material ground, preferably to a fine powder. The powder so produced may be mixed with water in a concentration of from about 1 to 8 per cent by weight to make a dispersion or solution which possesses suitable non-penetrat ing characteristics. Another type of non-penetrating liquid mixture having gel-like characteristics may be made by mixing from 3 to 5 per cent of certain soaps, such as aluminum stearate and aluminum palmitate, with liquids, such as kerosene, gasoline and benzene, and preferably crude oil because of its cheapness, and then heating the mixture to from 50 to C. After cool- Among the advantages of the invention are that openings may be made much farther into the surrounding formation due to the fact that it is unnecessary to penetrate through both the metal casing and cement liner surrounding it, as is necessary in a conventional treatment, thus giving greatly improved results as regards in-- creased yield from the well. In addition, in the treatment according to my improved method, it-

is unnecessary to use a metal casing long enough to extend to the bottom of a producing formation.

This application is a continuation-impart or my co-pending application, Serial No. 21-21769, filed June 9, 1938.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a method of providing a channeled supporting wall for a well bore penetrating a fluid producing formation, the steps which consist in depositing in the pores of the formation a liquid sealing mixture characterized by having a ready penetration into the fine .pores of an earth orrock formation which are so small as to prevent the penetration of cement slurry therein to, and thereafter forming flow channels in said formation by explosive means.

2. in. a method of providing a channeled supporting wall for a well bore penetrating a. fluidproduoing formation, the steps which consist in introducing into the well bore a liquid siiiealte mixture of the type which is of itself capable of spontaneous transformation into a firm gel after a time in an amount sufficient to fill the well bone to 'a point above the producing formation, thereafter introducing into the well bore a. quantity of a non-penetrating liquid mixture and applying pressure thereto whereby the Iliquid mixture is displaced into the formation immediately surrounding the Wei-1 'bore, allowing said liquid silicate mixture to solidify, removing from the well bore the non-penetrating liquid mixture previously introduced, and thereafter forming flow channels in the formation by explosive means.

3. In a method of providing a channeled supporting wall for a well bore penetrating a fluidproducing formation, the steps which consist in introducing into the, well bore a liquid silicate mixture of the type which is of itself capable of spontaneous transformation into a firm gei amter a time in an amount suiiicient to fili the well bore to a point above the producing formation, thereafter introducing into the well bore a quantity of a non-penetrating liquid mixture and applying pressure thereto whereby the liquid silicelte mixture is displaced into the formation immediately surrounding the well bore, allowing said iiquid silicate mixture to solidify, removing from the well bore the non-penetrating liquid mixture previously introduced, and thereafter perforating the formation with a gun perforator to permit the e of fluids therethrough to the well.

CARL F. PRUTION. 

